1. Field of the Invention
The present invention relates to a cleaning device; an image forming apparatus, such as a copier, a printer, or a facsimile, including the cleaning device; and a process cartridge including the cleaning device.
2. Description of the Background
Image forming apparatuses are used as copiers, facsimile machines, printers, and multi-functional devices combining several of the foregoing capabilities, including electrophotographic image forming apparatuses.
Typically, such electrophotographic image forming apparatuses have a cleaning device to remove excess or residual toner remaining on a surface of an image bearing member after transferring a toner image from the image bearing member, such as a latent image bearing member or an intermediate transfer body.
For such cleaning device, a blade system that scrapes away excess toner with a cleaning blade is extensively used because of its simple configuration and excellent cleaning performance. Such blade system is capable of mechanically scraping the surface of an image bearing member with relatively great force, thereby effectively preventing so-called “filming”. Here, the term “filming” refers to a phenomenon in which additives such as silica and zinc stearate are detached from a toner body due to mechanical stress during an image forming process and are attached to the surface of the image bearing member to form a thin film. Such filming may reduce the adhesion force of toner to the surface of the image bearing member, thereby resulting in an image failure such as image flow.
Recently, many attempts have been made to reduce the particle diameter of toner in order to obtain higher image quality. In particular, certain types of toner particles are formed in a substantially round shape by a polymerization method to reduce cost. Such substantially round-shaped toner (hereinafter “round toner”) has certain advantages, such as relatively high transfer efficiency, over a conventional type of ground toner (hereinafter, “irregular toner”). As a result, such round toner may simultaneously satisfy the demand for high image quality and reduce the amount of toner discarded as residual toner.
However, when such minute and/or round toner is cleaned with a blade system as described above, it may be difficult to completely scrape off such toner with a cleaning blade because a certain portion of the toner particles passes under the cleaning blade. In such case, the cleaning blade needs to be pressed against a surface of an image bearing member with relatively greater force than when irregular toner is used. Accordingly, the cleaning blade and/or the surface of the image bearing member may be further abraded, thereby reducing the service life of the cleaning blade and/or the image bearing member. Consequently, such abrasion may also increase the driving load on the drive mechanism for moving the surface of the image bearing member, which is undesirable.
One method of effectively cleaning such minute and/or round toner proposes using an electrostatic cleaning system to clean such toner remaining on the surface of the image bearing member by electrostatic action. A description of such electrostatic action is given below, with reference to FIG. 1.
In this regard, a typical electrophotographic image forming apparatus generally supplies a bias of a polarity opposite a (normal) polarity of toner attached to a surface of an image bearing member so as to transfer the toner on the surface of the image bearing member onto a transfer member, such as a recording medium. As a result, residual toner remaining on the surface of the image bearing member after the transfer process may include both normal-polarity toner and opposite-polarity toner, as shown in a low charge area of FIG. 1. In such case, when employing the electrostatic cleaning method, such image forming apparatus must be capable of electrostatically collecting both the normal-polarity toner and opposite-polarity toner.
FIG. 2 is a schematic view illustrating a conventional type of cleaning device 170 employing an electrostatic cleaning system.
In FIG. 2, the cleaning device 170 has a first conductive brush roller 171 to which a voltage of positive polarity is applied and a second conductive brush roller 172 to which a voltage of negative polarity is applied. In the cleaning device 170, the first conductive brush roller 171 and the second conductive brush roller 172 are arranged along a travel direction of a surface of a photoconductor 1a functioning as an image bearing member. The first conductive brush roller 171 removes negatively charged toner, and the second conductive brush roller 172 removes positively charged toner. Then, the toner attached to the brush rollers 171 and 172 is removed by collection rollers 173 and 174, respectively. The toner attached to the collection rollers 173 and 174 is then removed from the surfaces of the collection rollers 173 and 174 with corresponding collection blades.
Alternatively, another conventional type of cleaning device is capable of cleaning both positive-polarity toner and negative-polarity toner with a single brush roller.
In such single-brush roller conventional cleaning device, a plurality of conductive bristles forming part of the brush roller includes a first area to which a bias of positive polarity is applied and a second area to which a bias of negative polarity is applied. Rotating the brush roller causes the first area of positive polarity and the second area of negative polarity to contact a surface of an image bearing member. Thus, negatively charged toner is removed by the first area, while positively charged toner is removed by the second area. The toner attached to the brush roller is removed from a surface of the brush roller with a collection roller. The toner attached to the collection roller is then removed from a surface of the collection roller with a collection-roller blade.
However, in the case of using such minute and/or round toner, when the toner attached to the surface of the collection member such as the collection roller is cleaned with the separation member such as the collection-roller blade, a problem similar to that of the above-described case where the toner on the photoconductor is cleaned with the cleaning blade may occur. That is, the separation member may not completely scrape away such toner, thereby resulting in a cleaning failure on the surface of the collection member. Such cleaning failure may reduce the collection efficiency of toner from the cleaning roller such as the brush roller, thereby reducing the cleaning performance of the cleaning member for the surface of the photoconductor. Therefore, it is necessary to prevent a cleaning failure of the surface of the collection member in some way.
Pressing the separation member against the surface of the collection member with a relatively greater force may enhance the cleaning performance of the separation member for the surface of the collection member, and thus, in the short term, a cleaning failure can be prevented from occurring when such minute and/or round toner is used. However, in such case, a large friction force may be generated between the separation member and the surface of the collection member, thereby resulting in further abrasion of the separation member and the surface of the collection member and a reduction in the friction coefficient therebetween. Consequently, in the long term, a portion of toner may pass between the separation member and the surface of the collection member, thereby resulting in a cleaning failure.
The above-described cleaning failure may also occur in, for example, a configuration in which toner attached to a movable surface of a cleaning member is collected with a smoothly movable surface of a collection member and then the toner attached to the surface of the collection member is removed by a separation member disposed to press against the surface of the collection member.
Accordingly, in such configuration, even when toner on a surface of an image bearing member is mechanically removed without applying a bias to the cleaning member having the movable surface, a cleaning failure similar to that described above may occur. Alternatively, for example, even when a surface moving member such as a recording-medium transport member is cleaned, a cleaning failure similar to that described above may occur.
Consequently, there remains a need for a cleaning device capable of preventing a cleaning failure from occurring on a surface of a collection member in the long term, and an image forming apparatus and a process cartridge including such cleaning device.